The present invention relates to robotic systems for use in automated laboratory applications, and more particularly to a liquid sensor for a filtration station for use in automated analytical laboratory systems. The liquid sensor detects when filtration of the liquid has completed, independently of the time required for the liquid to be filtered, by detecting when the liquid has finished passing through the filter in the filtration station.
Automation in analytical laboratories is not, of itself, a new concept, but instead has been widely practiced for many years. More recently, it has appeared mainly in the form of microprocessor controlled analytical instrumentation with dedicated hardware, such as auto samplers, continuous flow systems, and computerized data collection, calculation, and report generation facilities. The very recent past has seen important improvements wherein laboratory automation has been extended by the use of robotics, combined with programmable computers, to new tasks which include sample preparation, and even entire analytical determinations. The first such robotic system was introduced in 1982 by Zymark Corporation (Hopkinton, Massachusetts). As experience has been gained with these systems, they have been successfully applied to ever more sophisticated laboratory operations, and the number of accessory components for specific tasks has grown accordingly.
Understandably, however, there is a great need for accessory modules and equipment which can provide sophisticated support operations in a robot-friendly manner. Tasks which are so trivial for a human operator that they essentially go unnoticed may prove to be all but insurmountable for a robotics system. Sometimes the most trivial and routine manual operations turn out to be the most intransigent when efforrs are made to perform then with robot-friendly modules and sensors. As a result, modules and sensors for performing many important tasks are still not yet commercially available.
An example has to do with the filtration of liquids, and in particular the filtration of a sample through an extremely fine filter for measuring suspended solids. Environmental Protection Agency requirements, such as in the EPA approved protocol specified in the manual procedure US EPA method 160.2, for the determination of total suspended solids (TSS) in water and waste water, is routinely performed at many manufacturing locations throughout the country, and in support of waste water treatment research and development studies. It is a routine EPS test procedure that is highly repetitive, usually involves a large number of samples to be analyzed, and requires the committed attention of the human analyst--a prime example of a procedure wherein robotic automation would be highly desirable.
For purposes of the present invention, it is not necessary to described the entire method and apparatus by which the total suspended solids may be determined in a robotic system, particularly because the liquid sensor of the present invention, as will be easily appreciated, can also be utilized in many other compatible robotics applications. The problem addressed by the present invention has to do with the sometimes highly variable amount of time required for a filtration step to take place, not only from one application or implementation to another, but often with the same procedural application itself.
In the context of the above-noted example, for instance, one liquid sample might have virtually no solids in suspension, while another might have a great deal. In both cases, the solids are understandably extremely small or they would not remain suspended, depending to some extent, of course, upon their density. Accordingly, the filter through which the liquid is passed will be extremely fine, and the liquid flow rate will be very slow. When the task is performed manually, the human operator has no difficulty in checking from time to time to observe when the filtration step has concluded. Such a seemingly trivial time-independent task, however, can present a formidable obstacle to the robotics system designer.
A need therefore remains for a liquid sensor for a filtration station for a robotics system for sensing when filtration of a liquid has completed, independently of the time required for the liquid to be filtered. Such a system should accurately detect when the liquid has finished passing through the filter in the filtration station such that liquids can be confidently filtered in the station substantially independently not only of time, but of vessel configuration, volume of liquid being filtered, and advantageously such that features such as a vacuum assist to accelerate the rate of filtration can be employed without interfering with the sensing and detection of conclusion of the filtration step. Further, detection should be non-intrusive and non-invasive to avoid contamination of the liquid.